Conical refractor



arm-44c April 21, 1959 TELL j D. S. TOFFOLO CONICAL REFRACTOR Filed Oct.24, 1955 INVENTOR DOMINIC S. TOFFOLO BY ATTORNEYS United States PatentCONICAL REFRACTOR Dominic S. Tolfolo, Camp Springs, Md.

Application October 24, 1955, Serial No. 542,533

1 Claim. (Cl. 88-1) (Granted under Title 35, US. Code (1952), see. 266)The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

The present invention relates to refractors and more particularly to arefractor which passes plane parallel incident radiation of a givenintensity to plane parallel radiation of greater intensity than theincident radiation.

The refractor comprises a radiation transparent medium presenting to theincident fiux an annular conical surface and having a second conicalsurface coaxial therewith through which the emergent flux passes. Theelement may be formed as a cone with a conical surface axially formed inthe base of the cone with elements parallel with the outer conesurfaces. In this case, the entrance cone surface may be centrallymasked to leave at its lower portion an annular conical incidentsurface. Peripheral incident flux is refracted to concentrate centrallyof the exit pupil at greatly increased intensity.

The refractor of this invention therefore afiords means of increasingthe intensity of an incident radiation source and further provides manyadvantages in optical and astronomical work. It may replacemulti-element lenses of a telescope wherein the same telescopic effectcan be obtained without the use of multiple lenses. The refractor may beinstalled in front of a light signalling device to increase theintensity of the signal, and by use of different materials in making therefractor, increases in intensity of radio frequency radiation can beobtained where the application of optical techniques is desired, such asantennas.

An object of the present invention is to increase the intensity ofincident radiation that passes through a refractor.

A further object of the present invention is to produce an element whichwill afford a desired emergent intensity related to the intensity ofplane parallel radiation incident on the element.

A still further object of the present invention is to provide arefractor which will effectively replace the use of multiple number ofexpensive optical lenses now used in optical equipment.

A final object of the present invention is to provide a refractor whichcan be made inexpensively as by molding or other means.

Other and more specific objects-of this invention will become apparentupon a careful consideration of the following detailed description whentaken together with the accompanying drawings, in which;

Fig. 1 is a side elevational view of the refractor diagrammaticallyillustrating the incident and emergent light rays.

Fig. 2 is a line projection from Fig. 1 illustrating the relationship ofthe areas covered by the incident plane parallel radiation and theemergent intensity.

Fig. 3 is a sectional view taken through the axis of the element toillustrate the cut-out portion of the cone shaped element.

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Referring now to the drawings there is illustrated in Fig. 1 one typicalembodiment of a refractor 10 comprising this invention. The refractor 10comprises preferably a single block of radiation retracting materialhaving similar cone shaped parallel outer and inner surfaces arranged toform a radiation entrance surface 11 and a radiation emergent surface12. The single block element may be formed in a solid cone shape andthen a similar cone shape cut axially from the solid block to form theemergent parallel surface or the refractor may be formed with a moldwherein the axially cone shaped inner surface may be formed by the mold.The vertex end 13 of the cone shaped element may be cut away alongdotted line 9 and the fiat end surface coated or masked with radiationabsorbing material which tends to prevent incidence through thatportion, or the vertex may be left uncut and coated or masked with anabsorbing material 8. The radius of the cone at the vertex end to becoated with absorbing material will be explained in detail later.

In many applications where precision requirements do not arise, such assystems for illuminating photocells or photosensitive crystals, theutilization device may present a sensitive area limited to theintensified exit pupil area and in such situations an uncoated orunmasked element may be used. The emergent rays away from the exit pupilpresents increasingly lower intensities which may be negligible in manyapplications. Only that radiation which strikes the inner surfaceemerges as parallel rays and those are the emergent rays that areconfined to an area having a greater intensity than the incidentintensity.

It is obvious from Snells law Sin 9 Sin where the refractor is in air,N=the index of refraction of the material forming the refractor, Sin 0is the angle of incidence, and Sin is the angle of refraction, if theincident radiation is plane parallel radiation and the incident andemergent surfaces are parallel then the incident radiation will passthrough the element and emerge as parallel radiation. It has beendetermined that a cone shaped element with any base angle and madeaccording to this invention will have an emergent intensity which isgreater than the incident intensity due to the incident radiation beingconfined to a smaller area by refraction caused by the material of theelement. There is a critical base angle which determines the surfaces ofthe element which will be formed by the least amount of material and yetpass incident radiation which will have the desired intensity onemerging from the element. This angle X" (Fig. l) is determined by theformula Cos (0)=N(l-Cot 0) where N is the index of refraction of thematerial forming the element, 0 is the incident angle, and 0 is therefracted angle for said incident radiation. It is to be noted that theincident angle 0 is numerically equal to the base angle X of the elementwhich is equal to the angle formed by the interception of a lineperpendicular to the outer surface 11 and a line perpendicular to thebase as shown in Fig. 1.

Since the cut-out cone portion has its surface 12 parallel to the outersurface 11 of the element, the base angle of the cut-out portion will bethe same as the base angle X" of the element. The incident radiationpasses through the element and emerges from surface 12 with a radiaitonintensity which is greater than the incident intensity. It does this bytwo refractions which are self correcting at any wave-length, thusmaking it achrm matic. If b is the radius of the circle at 15 formed bythe outer extremities of the incident radiation which will be refractedas parallel rays by the surface of the cutaway cone portion, r is theradius of the inner cutaway cone at the base, and a is the radius of thetop portion of the element which is coated with a light absorbingmaterial, then the usable incident light is contained within the conicalsurface bounded by b and a (Fig. 1) and it can be shown that b=a+r. Theincident intensity has a direct relationship to the emergent intensityand is related according to the formula emergent intensity incidentintensity r for intensity amplification. The radius a is made such thatthe plane parallel incident radiation striking the refractor at thebeginning of the uncoated surface at the top porion of the element willenter the element and be refracted to the top point of the cutaway coneportion, to be refracted again as parallel radiation. All incidentradiation striking the refractor away from the radiation absorbingmaterial will be refracted inwardly toward the cutaway cone and willagain be refracted on emerging therefrom but will be confined to asmaller area than the incident light whereby the intensity will begreater.

Fig. 1 illustrates a bundle of plane parallel light rays entering thesurface 11 and refracted toward the surface 12 wherein the rays areagain refracted as parallel emergent rays. The emerging rays will beparallel with the incident rays and confined to a smaller bundle whichis confined within the circle having a radius of r, Fig. 2, the usablelight area after passing through the optical element.

In making a refractor of the present invention, the element may be madeof glass, or a more readily moldable material of which there are manysuitable clear plastics on the market which can be used, also, in caseof use with X-rays the element can be made of wax, such as paraflin. Therefractor of this invention may be used for many purposes in increasingthe intensity of incident radiation and is bound by the index offraction of the specific material which is used for the specificradiation to get the proper angle of refraction for the greatestemergent intensity, that is, for optical elements which are formed fromthe minimum amount of material. For refractors having base angles notdetermined by the above formula, the base angles will be equal to theangle of incidence but the amount of material forming the refractor willbe greater than the material used when the refractor is made accordingto the above formula.

The values for forming the refractor can be determined by choosing theratio of emergent intensity and incident light and the desired radius bformed by the extremity of the bundle of rays desired to be used. Fromthe formula as given above, where the base angle is equal to 0. Thisformula is used only to determine the base angle for an element in whichthe minimum amount of material is to be used. For elements in which theamount of material is of no concern, the desired intensity ratio can beobtained as illustrated above for any chosen radius of incidentradiation and the desired intensity ratio.

For illustrative purposes an element having an index of refraction of1.5 and formed in accordance with the present invention for an emergentintensity three times the incident intensity that has a radius b of 3cm. for the incident radiation is shown in Fig. 1. From the formulaemergent intensity 2b incident intensity r it is determined that theemergent pupil r will be 1.5 cm., thus the radius a of the circle at thevertex end that is coated with radiation absorption material is 1.5 cm.This determines the dimensions of the various functional parts of theelement. Now, for the angle in which the least amount of material willbe used, the formula Cos (0)=N(l-Cot 0) is used, and it is determinedfor an index of refraction of 1.5 the angle x (Fig. l) is 583". For adifferent index of refraction, the angle x will be different. An elementmade in accordance with the above disclosure will make a good telescopeand could be used for other purposes where incident radiation is to beincreased and confined to a specific area.

The vertex end 13 and the surface portion 16 of the element below 15Fig. 1 may be coated with a light absorbing material 8 or either cutaway and then coated to prevent interference by light which normallywould enter those portions of the element. The surface below 15 (Fig. 1)if cut should be cut perpendicular to the base of the element to preventthe possibility of interference with the usable light passing throughthe lens. A refractor made in accordance with this invention may be usedto replace multiple lens devices now used in the optical field. Such anelement makes a good telescope, it can be used to increase the intensityof X-rays, increase light intensity for photo-detectors, increase theintensity of light signalling devices and many other applications whichwill be obvious to those skilled in the art.

0bviously many modifications and variations of the present invention arepossible in the light of the above teaching. It is therefore to beunderstood, that within the scope of the appended claim, the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

A single achromatic refractor comprising a solid cone shaped body ofradiation transparent material having similar cone shaped parallel outerand inner surfaces having a common base and arranged to form a radiationentrance surface and a radiation emergent surface, said inner surfacebeing formed by cutting a cone shaped surface extending axially andinwardly from the base of said radiation transparent material, said coneshaped body having a base angle equal to an angle formed by theinterception of a line perpendicular to said outer surface and a lineperpendicular to the base whereby the latter angle is equal to an angleof incidence of plane parallel incident radiation along the lineperpendicular to the base, said base angle being formed by the formulawhere 0 is the angle of incidence of plane parallel radiation, is theangle of refraction, and N is the index of refraction of the radiationtransparent material, said outer surface having a central portionthereof coated with a radiation absorbing material and adapted to permitpassage of only peripheral incident plane parallel radiation which willbe refracted toward the axis and emerge from said inner parallel surfaceformed by the axially cut-out cone shaped surface whereby only radiationincident on the unccated surface will emerge from the inner parallelsurface as a central circular beam of plane parallel radiation ofcircular form and with a greater intensity than said incident radiation.

(References on following page) References Cited in the file of thispatent UNITED STATES PATENTS Anthony Nov. 21, 1905 Leventhal Aug. 11,1931 Rivier Oct. 27, 1936 Thomas Mar. 28, 1939 Thomas July 29, 1941Kellogg Feb. 16, 1943 6 Benford June 20, 1944 Hayward July 11, 1950Bouwers Jan. 28, 1958 FOREIGN PATENTS Great Britain of 1909 GreatBritain Sept. 17, 1935 France Feb. 18, 1935 France Nov. 26, 1952

